Project Summary/Abstract Cancer is a complex landscape of aberrant cell signaling programs, initiated by oncogenes. The causal oncogene drives the preponderance of accumulated mutations that enable tumorigenesis. Cancers arising this way can be reliant on the initiating oncogene, a term known as oncogene addiction. The proto-oncogene c- MYC is a transcription factor that regulates much of the genome and is deregulated in many cancers. The transgenic E-tTA/Tet-O-MYC mouse model of T-cell acute lymphoblastic leukemia (T-ALL), allows for modulation of c-MYC expression (ON vs OFF). When c-MYC is expressed T-ALL progression is observed, and when c-MYC expression is revoked tumor regression occurs. Using cells and microarray data from this model we employed a nested effects model (NEM) that infers hierarchical relationships anchored to master transcription factors that govern critical aspects of cell biology. We identified a critical node governed by a class of histone demethylases influencing transcriptional availability across the genome. KDM5B/JARID1b is known as a transcriptional repressor, and is downregulated in the T- ALL model when c-MYC is overexpressed. Using CRISPR/Cas9 mediated mutagenesis to disrupt KDM5B expression, we observed a potent reduction in cell death when c-MYC expression is abrogated; suggesting KDM5B mediates cell death responses in T-ALL. The central hypothesis is that KDM5B acts as a tumor suppressor in c-MYC-dependent T-ALL. We propose the following three aims to test this hypothesis. Aim 1 will determine if c-MYC directly suppresses KDM5B expression and whether this is critical in c- MYC-dependent T-ALL. Chromatin Immunoprecipitation (ChIP) of c-MYC at the promoter regions of KDM5B will identify whether direct regulation is required. Aim 2 will identify the mechanism through which KDM5B regulates cell survival in c-MYC-dependent T-ALL. Using RNA-seq and ChIP-seq approaches we will uncover critical c-MYC and KDM5B regulated gene programs and dissect the pathways unique to KDM5B. Aim 3 will discover how KDM5B influences tumor development in vivo. Genetically modified cell lines that over-express KDM5B as well as KDM5B knockout cells will be injected into syngeneic hosts to determine KDM5B influence on tumor development in vivo. Preliminary data suggests that lymphoma cells treated with the bromodomain inhibitor JQ1 undergo cell death only if c-MYC is downregulated and KDM5B is upregulated. Human T-ALL cell lines responsive to JQ1 will be injected into NOD-SCIDIL-2Rg-/- (NSG) mice and tumor progression will be tracked by bioluminescent imaging (BLI). Additionally, primary human lymphoma samples will be injected into NDG mice and treated with the BET inhibitor JQ1. These studies are the basis of an independent research program and demonstrate a novel paradigm in understanding how c-MYC promotes tumor development through repression of a tumor suppressive epigenetic landscape regulated by KDM5B, and identify therapeutic options for treating c-MYC-induced T-ALL. !